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SMARAGD – The Study of Mineral Alterations of Clay Barriers Used for
Radwaste Storage and its Geological Diposal
Summary
Miroslav Honty 1 , Mieke De Craen 1 , Maarten Van Geet 2
1 SCK·CEN, Belgium
2 NIRAS·ONDRAF, Belgium
The SMARAGD was a 2-years postdoctoral fellowship (2006-2007) funded under EURA-
TOM programme of EC in order to study mineral alterations of Boom Clay trigerred by geochemical
perturbations. In Belgium, the Boom Clay is studied as a reference host formation
for research purposes and for the assessment of deep disposal of high-level radioactive waste.
The geochemical perturbations may alter the favourable properties of Boom Clay which are
necessary to fulfill the required safety functions (De Preter, 2007 [1]). Within the SMARAGD
project, two types of geochemical perturbations were considered: oxidation due to ventilation
of underground galleries and the alkaline plume effects due to application of concrete both in
the gallery lining and as a part of the waste package design. The oxidation effects were studied
in situ in the HADES URL facility in Mol, Belgium. The core samples taken from the
Connecting Gallery (ventilated since 2001) and the Test Drift (ventilated since 1987) provided
a unique opportunity to study the oxidation effects at different time scales. The alkaline plume
effects were studied in the laboratory as a batch experiment under well constrained conditions
in terms of temperature, Eh, pH and leachate chemistry evolution. The results of the
SMARAGD project will serve as an input data for modelling long-term performance of the
geological barrier as well as the key parameters to calibrate the existing models. The results
generated during SMARAGD project are complementary to those of ECOCLAY II (2000-
2003) dealing with the effects of cement on clay barrier performance and NF-PRO (2004-
2007), which was investigating the oxidation as one of the key processes affecting the longterm
barrier performance in the near-field.
1. Introduction
The geochemical perturbations occur as a result of construction and operation of the underground
facilities such as URL and/or final high-level waste repository. The geochemical perturbations may
alter the in-situ pH and Eh conditions followed by the change in the pore water chemistry and mineralogy
of Boom Clay. Due to excavation of shafts and galleries, the host rock is inevitably exposed
to atmosphere and Eh will start to increase. The pyrite, one of the most active redox-sensitive mineral
in the Boom Clay, will be oxidized. The side-products of this reaction involve H + generating
acidity (pH decrease), sulphates, thiosulphates, and Fe 3+ precipitates. The reduced sulphur species
are of major concern, because of their highly corrosive effect on the metallic overpack of canisters
with radioactive waste. The acidity might trigger the corrosion of the concrete, moreover, most of the
radionuclides are more mobile under low pH conditions.
The cement, which is present in the concrete gallery lining and also as a principal component in the
current supercontainer design (Wickham, 2005 [2]), is the source of aggressive alkaline fluids when
in the saturated state. The pore fluids released from water-saturated concrete typically range in pH
511